Mate Monopolization by a Dominant Male in a Multi-male Social Group of a Mouthbrooding Cichlid, Ctenochromis horei

Abstract

Spacing behavior, feeding habits, social interactions and breeding behavior of a mouthbrooding cichlid, Ctenochromis horei, were investigated in Lake Tanganyika. About 60-70 individuals found in a 15m×9m vegetated patch had a nearly equal sex ratio. Most fish remained for more than 3 months, limiting movements, foraging, mating and brooding, to the patch. They formed a stable group with well-overlapping home ranges and foraged in schools. Attack and avoidance behavior among large males indicated a dominance order positively correlated with body size. Replacement of the most dominant male in group occurred twice during the 6-month observation period. All observed matings were monopolized by the dominant male, although apparent sneaking behavior by other males occurred during mating. Mating monopolization was accomplished by the dominant male defending a female from rivals for several hours before and during spawning. These observations suggested that the mating system of C. horei is polygynous. Only females mouthbrooded the eggs and larvae, and later guarded the juveniles. The spacing behavior of C. horei appears to be responsible for its mating system, which contrasts with those so far reported for other mouthbrooding cichlids.